This book was originally published in 1986 and Amazon.co.uk lists a March 31st 2006 reprinting under Transformation of Consciousness. If you want to read more of Ken Wilber's epicyclic models, then this is twenty year old epicycles (see Andresen and Forman: Cognitive Models and Spiritual Maps for a more recent Wilber piece followed by a sympathetic but still exposing critique by Christian de Quincey). Wilber's old friend Michael Bauwens has put up his The Cult of Ken Wilber on the web for those interested in this New Age cult.
This book is worth the money primarily due to Harvard psychologist Professor Daniel Brown's extremely important chapter with its examination of the parallels between the stages of meditation in three authoritative yogic traditions (Yoga Sutras, Vipassana and Mahamudra). Although Brown came to the odd conclusion that all the paths are same but the goals different, others like myself (also Forman in The Problem of Pure Consciousness)disagree as the key stage is Basis Enlightenment (nondual Pure Consciousness) is the stage all 3 describe most similarly. Post-Enlightenment practises differ.
Brown's study discusses the yogic experience of the subtle flow of the Light when mental processes are held in abeyance. The Light is perceived as coming in waves (Hindu) or pulses/moments (Buddhists) which is clearly just a difference in focus. The YS tradition describes the Light as the coordinates of that previous gross mental content or A CONTINUOUSLY VIBRATING ENERGY FIELD IN A STATE OF CONTINUOUS WAVE PROPAGATION.
This information proved critical in my 1994 identification of the physical correlate of the Divine Light/Pure Consciousness or Godhead with the brainwaves from the brainstem Reticular Activating System. These brainwaves continuously underly all other brainwave activity and only cease at death. Numerous other authoritative yogic and mystic facts (the Light at the Centre, the prana/atman identity, Advaita's mutual superimposition of Pure Consciousness and sense percepts, Insight meditation's catching the Light in gaps between percepts, Vajrayana's Clear Light of Death as a continuous series of moments etc.) plus the presence of the Light in NDEs fits this interpretation (see my review of Kapstein's The Presence of Light on Amazon.com) or The Oneness/Otherness Mystery: The Synthesis of Science and Mysticism. Patanjali even begins the Yoga Sutras stating: yogas cittavritti nirodhah (yoga is the cessation of the WAVE-LIKE FLUCTUATIONS of the mindstuff). See also Travis's model of Pure Consciousness as the background state in Dalai Lama and Varela: Sleeping, Dreaming and Dying. The RAS is well known as it arouses the cortex as distinct from specific attention and is a universal human process unaffected by culture and tradition. Cessation of the RAS constitutes brain death.
Sutapas Bhattacharya

just one personal comment: merely reading the definitions of "split life-goals" and "dark night of the soul" by Wilber saved me several months (years?) of struggling - the book provides a novel structure of psychopathology and if you have a structure you have something to hold onto. very therapeutic book for (post)existential-level strugglers!
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i really like the brief and concrete style of the older books by Wilber (Atman Project is my favourite!), although, according to Wilber himself, they contain slightly outdated ideas. don't start with it, but don't forget it!